The present invention relates generally to laser repair of electronic devices that include arrays of discrete circuits, any one of which may be isolated in the event that the discrete circuit is defective, and relates in particular to the repair of liquid crystal display panels.
Liquid crystal display (LCD) panels may generally include liquid crystal layer sandwiched between glass plate structures, one of which includes an array of transistor elements (having signal lines and gate lines) in a substantially transparent electrode layer. The other glass plate structure generally includes a large number of sets of color filters (e.g., red green and blue) forming color display pixels.
It is known that individual transistor elements may be defective upon manufacturing. The defects may cause the pixel to remain dark even when it is turned on, or may cause the pixel to remain bright when power is applied to the display panel but the pixel is turned off. It is further known that a dark pixel is not a considerable problem, as the human eye will likely not notice a tiny pixel in an overall panel failing to turn on. On the other hand, a bright pixel when it is intended to be dark is quite noticeable. Many procedures have been developed for attempting to reduce or eliminate the bright pixel defects.
U.S. Pat. Nos. 6,812,992; 7,502,094; and 7,755,380 for example, generally disclose using laser radiation to decrease the transmittance of the color filter of a damaged pixel. U.S. Pat. No. 5,142,386 discloses using laser radiation to disturb the orientation of the liquid crystal molecules, and to blacken the color filter of a damaged pixel. Other techniques involve cutting conductive portions of the transistor elements associated with the pixel to be repaired.
U.S. Pat. No. 7,636,148 discloses the use of a repair film (a transparent organic film) that is coated on the exposed outer surface of the device, wherein the repair film is specially designed to become opaque upon application of associated laser radiation. U.S. Pat. No. 7,697,108 disclose the darkening of damaged pixels by 1) forming a recess in the outer substrate aligned with the defective pixel, 2) depositing a UV curable resin in the recess, and 3) irradiating the resin with ultraviolet radiation.
The individual pixels (e.g., as defined by the color filters) do not contact one another, but are generally each surrounded by a black matrix material. U.S. Patent Application No. 2009/0141231 disclose darkening damaged pixels by applying laser radiation to portions of the black matrix to cause black matrix particles to become dispersed between the pigment layer and an upper substrate to thereby occlude the pixel. The reference also discloses using UV radiation to destroy the associated alignment layer to cause the liquid crystal molecules to become misaligned.
It is also known that applying laser radiation to films within a pixel may cause bubbles to be formed that may migrate to other regions of the liquid crystal panel compromising the functionality of neighboring pixels. U.S. Patent Application Publication No. 2006/0087321, for example, discloses using laser radiation to disrupt alignment films of damages pixels, and further that the repetition rate of the laser is controlled to provide that any bubble formed by the radiation is immediately targeted with another laser beam. The reference discloses that when the second laser energy hits the pixel that includes such a bubble, the laser illumination energy is mostly absorbed by alignment films, causing them to become evaporated. The evaporated components are disclosed to drift within the bubble and eventually settle as a dark film, decreasing the amount of light that passes through.
Many liquid crystal displays include a polarizing film or plate on at least the outer surface of the display device. The polarizing film or plate provides desired display viewing functionality, and may include a wide variety of polarization orientations at different portions of the film or plate. In devices that employ polarizing films or plates on an outer surface of the device, the pixel repair process is further complicated in that the varying polarization orientations will result in varying amounts of polarized laser energy being applied to defective pixels.
Although many procedures have been developed for darkening defective pixels in a liquid crystal display, there remains a need for such a system and method that overcomes drawbacks of conventional methods, such as for example, the difficulty in managing entrapped bubbles when the liquid crystal molecules are disturbed, and the difficulty in performing the processing steps when polarization films are employed in the liquid crystal display.